A sophisticated X-ray technology paves the way to uncover the secrets of a 380 years old Rembrandt masterpiece. Underneath the “Old Man in Military Costume” painted by the Dutch artist in the years 1630/31, earlier investigations spotted another portrait which was only faintly distinguishable with all applied technologies. For years, art historians puzzled over the question of who is depicted on the repainted picture. An international team of scientists now used a detailed mock-up to test different methods to look beneath the original painting at DESYs X-ray source DORIS and at the National Synchrotron Light Source (NSLS) of the Brookhaven National Laboratory (BNL) in the United States, as well as with a mobile X-ray scanner. The results are published as the cover story of the "Journal of Analytical Atomic Spectrometry" (JAAS) of the British Royal Society of Chemistry.